The present invention relates generally to tooling and a process for inserting, rearranging and/or removing the control rods in a boiling water reactor pressure vessel.
The control rods in a boiling water reactor contain an absorbent material that when positioned in the reactor core can be used to slow the fission rate of the nuclear fuel. However, the absorbent material is subject to degradation after extended use. Therefore, it is periodically necessary to replace the control rods. Since different regions of the reactor core have different levels of irradiation fluence, in order to reduce expenses, it is common to periodically reposition the control rods within the core to maximize their useful life.
In order to pull a control rod out of its associated core location, it is also necessary to pull out the associated fuel support since the control rod's velocity limiter cannot slide past an installed fuel support. Therefore, the tools commonly used to reposition and/or replace the control rods include a first grapple for lifting the fuel support. A second grapple is then used for uncoupling the control rod from its associated control rod drive and lifting the uncoupled control rod. Operators that use just these two tools have been known to occasionally drop the control rod. Therefore, a third grapple tool is often used to grab the top bail handle of the control rod when the control rod is being lifted.
When the control rods are being rearranged, it is customary to set the fuel support on the reactor pool floor in a sheltered area. The control rod is then taken out of the pressure vessel and placed in a fuel pool located adjacent the pressure vessel. When the control rod is to be reinserted, it must be transferred back from the fuel pool to the pressure vessel. When the fuel support is to be reinserted, it must be picked up from the floor. These transferring motions take a relatively long time and in the case of the control rods result in the undesirable exposure of a radioactive component.